Multi-line chat system for Apple IIs, required multiple phone lines. Very
popular chat system starting in 1985, continues with a hard core group
of folks at the website listed below (ddial.com). Later ported to IBM
Compatibles.

Daniel Bowers describes ddial this way: "DiversiDial (DDial) was software
from 1984(?) by Bill Basham for the Apple ][ that allowed 7 modems to
simultaneously connect to 1 computer to chat. It suppored 300 baud modems.
One of the 7 'slots' could also be used to connect via POTS to other similar
machines, yielding vast (for the time) networks of chat rooms that flourished
in the US from 1985 - 1990 or so. It described itself as "CB for the
computer". (In fact, you could jerry-rig the Apple's joystick port and get
an 8th modem to work.) Many chat-related concepts we use today were found
(but probably not invented) there -- emoticons, phreaking (to pay the
horrendous phone bills), channel owners (called 'co's, actually short
for co-sysop), etc."

Jim Meyer says: " DiversiDial (DDial for
short), an early Apple II CB simulator that worked by filling an Apple
II with modems. Later versions could run across two machines, bridged by
hardware, allowing 12 people (14 including both consoles) to chat at a
time, as well as the ability to have one system call another and pass
traffic between them (called "Links"). Most others charged flat rates
of $15 or $20 per month; some had a basic and advanced price,
differentiated by how long you could chat before "timing out" and being
logged off, or how long you had to wait after
timing out before you were allowed to log in again. The author, Bill
Whose-last-name-I-forget, ran one or two in Houston, Texas; one of them,
PennyNet, was so-named for its penny-a-minute rate.
DDial was very popular in Texas in the mid-80s; there were DDials in
Houston, Dallas, Austin, Corpus Christi. There was definitely one in
Detroit, Michigan; I seem to recall other states as well, but not
clearly.
Before the linking feature was introduced, some users would call long
distance to chat with people in other cities. This often led to long
distance visits, parties, and romances (for myself included)."